We had a drain valve that would not turn on the fresh water tank awhile back so I installed a new one and thought all was well. We had filled the tank last week for a short getaway but stayed home because of rain.
I went out tonight to drain the water out & nothing comes out. I tried to blow back through the valve & couldn't. I took the valve clear off & water still won't run out. Anyone got any ideas? It is a 308FBS

This is another interesting case of where did all the water go? I'm not familiar with your trailer but did you try opening a faucet to see if that made a difference? I know my new Jayco has a overflow line which my last trailer did not. I would be interested in how you manage to fix this if you don't mind posting again. In a funny kind of way, this is part of why I enjoy trailering. Until I got cancer 6 years ago I use to work in the maintenance dept of a major hospital. I was part of what was called the rapid response team. The idea was if one of us weren't able to fix a problem within an hour we would dispatch the work to the respective dept. In trailering one has electrical,mechanical,plumbing to figure out if something goes wrong. In between all that there is the enjoyment of being with family and going to places you've never been before. Good luck and hope you figure it out.
Richard